The impact of dust in the Saharan Air Layer (SAL) acting as cloud condensation nuclei (CCN) on the evolution of a tropical cyclone (TC) was examined by conducting simulations initialized with an idealized pre-TC mesoscale convective vortex (MCV) using the Regional Atmospheric Modeling System (RAMS). Two groups of simulations initialized with either a strong MCV or a weak MCV were conducted. In each group, there are five simulations with the maximum CCN concentration varying from 100, 500, 1000, 1500 and 2000 cm^-3 in a layer between 1 and 5 km, where the dust in the SAL are typically found.
Within each group of simulations, the MCVs showed similar evolution cycles in terms of the starting time of rapid intensification and occurrence of spiral rainbands. The starting time of rapid storm intensification and intensity divergence among simulations with various CCN concentrations were 24 hours earlier in the strong vortex experiment compared to the weak vortex one. Through the simulation period, both experiments showed a maximum difference in the azimuthally averaged surface wind speed about 20 m s^-1 among simulations. The storm intensities did not show a monotonic trend with increasing or decreasing initial CCN concentration. Most CCN within a 40 km radius from the center, where the eyewall formed, had been depleted by 24 hr. Increasing environment CCN led to an increase of the cloud droplet number concentration and a decrease of cloud droplet diameter outside of the major eyewall area. Latent heating due to important microphysical processes were analyzed. Dust in the SAL as CCN influenced the TC development by inducing changes in the hydrometeor properties, modifying the storm diabatic heating distribution and thermodynamic structure, and ultimately influencing the TC intensity through complex dynamical responses.
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